Optical elements using refraction (mainly made of glass) have frequently been used for general optical systems, in order to improve optical performance, particularly image formation performance with decreasing amount of aberrations. However aberration correction flexibility must be improved in order to sufficiently decrease Seidel's five aberrations and chromatic aberration on reference spectral lines, and because of this, the number, size and weight of the optical elements often increase.
To prevent this, an eye piece (optical system) where a plano convex shaped first lens and a plano convex shaped second lens are disposed, in a state of respective convex surfaces facing each other, and a diffractive grating surface is formed on one of the optical surfaces of the first lens and second lens has been proposed (e.g. see Japanese Patent Application Laid-Open No. H11-38330). Thereby an eye piece in which lateral chromatic aberration is well corrected can be obtained with a simple configuration of a small number of lenses, while insuring a predetermined eye relief.